Routing: avoid division by zero when vehicle capacity is zero

[vitor1001]

In get_preferred_order_of_vehicles, guard against division by zero when curr_vehicle_info.capacities[d] is zero.

Description

Issue

Checklist

• I am familiar with the Contributing Guidelines.
• Testing
  • New or existing tests cover these changes
  • Added tests
  • Created an issue to follow-up
  • NA
• Documentation
  • The documentation is up to date with these changes
  • Added new documentation
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• cpp/src/routing/problem/problem.cu

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• cpp/src/routing/problem/problem.cu

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📝 Walkthrough

Walkthrough

The vehicle ordering logic marks buckets with positive demand and zero capacity as infeasible. It assigns zero cost effectiveness and excludes those buckets from further cost calculations. Positive-capacity and zero-demand behavior remains unchanged.

Changes

Routing capacity calculation

Layer / File(s)	Summary
Capacity requirement guard cpp/src/routing/problem/problem.cu	Positive-demand buckets with zero capacity are marked infeasible and assigned zero cost effectiveness. Positive-capacity calculations and zero-demand behavior remain unchanged.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 6b5ea

The zero-capacity guard addresses the stated infeasibility case without any identified remaining merge risk.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing division by zero when vehicle capacity is zero.
Description check	✅ Passed	The description identifies the affected function and explains that the change guards against division by zero for zero vehicle capacity. The remaining template content does not make the description un…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 2

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Inline comments:
In `@cpp/src/routing/problem/problem.cu`:
- Around line 203-206: Update the capacity handling around
num_vehicles_needed_from_bucket so positive demands with zero
curr_vehicle_info.capacities[d] mark the bucket infeasible, using zero cost
effectiveness or the existing exclusion mechanism while retaining the division
guard. Preserve current behavior for zero demand and positive capacities.
- Around line 203-206: Add unit tests under the existing cpp/src/tests patterns
for the capacity calculation in the routing logic: verify positive demand with
zero capacity is safely guarded, and verify positive capacity preserves the
existing vehicle-count calculation. Use the relevant routing test fixtures and
symbols already established in the test suite.

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• cpp/src/routing/problem/problem.cu

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